The present invention relates to an image forming apparatus such as a copying machine, a printer, and a facsimile machine using electrophotographic method.
In recent years, image forming apparatuses such as copying machines, printers, and facsimile machines using electrophotographic method are used in various fields.
Most of the above image forming apparatuses are provided with fixing units to melt and fix a toner image onto a sheet by heat.
Such fixing units carries out a fixing process through a nip section configured with rollers or belts arranged to face one another by heat while conveying the sheet carrying the toner image thereon.
A countermeasure to prevent the fixing unit having a heating section and a vicinity thereof from heating are needed, since the heating unit is subject to high temperature.
As the countermeasures to prevent the fixing unit from heating, for example, there is suggested to provide a ventilation flue to supply cool air and to control the air by turning on and off a fan (for example refer to Patent document 1: Unexamined Japanese Patent Application Publication No. H7-181874).
However, it is difficult to completely prevent air inside the image forming apparatus from rising in temperature due to heat generated by the fixing unit or to prevent each device related to image forming provided in the apparatus from rising in temperature.
The above problem is a serious problem for a high speed image forming apparatus used for a consecutive long-haul image forming job.
There is publicly known a high speed image forming apparatus having a transfer unit to transfer a toner image, formed on an image carrier such as a photoconductive member or intermediate transfer member, onto the sheet through a transfer roller or a transfer belt disposed to face the image carrier.
When temperature of the transfer unit is raised by the heat propagated from the fixing unit, temperature of the image carrier in direct contact with the transfer unit raises immediately and eventually, temperature of developer and a development device is raised which results in deterioration of image quality.
Also, the transfer unit used for a high speed image forming apparatus is often provided with a transfer cleaning section to remove toner adhered on the transfer roller or the transfer belt.
When the temperature of the transfer cleaning section raises, packing of waste toner occurs.
To prevent occurrence of the above problems, a cooling device becomes necessary to suppress raise in temperature of the transfer units, however such countermeasure tends to increase cost.
Patent Document: Unexamined Japanese Patent Application Publication No. H7-181874
In view of the above problems, an object of the present invention is to realize the cooling device to effectively suppress raise in temperature of the transfer unit of the image forming apparatus and excessive raise in temperature of the fixing unit without the cost being raised.